In a class of 27 students, 10 have a brother and 12 have a sister. There are 4 students who have a brother and a sister. What is the probability that a student who has a sister also has a brother?

1/3

Step-by-step explanation:

10 students have a brother.

12 students have a sister.

4 students have a brother and a sister.

6 students have only a brother.

8 students have only a sister.

4 students have a brother and a sister.

Given that a student has a sister, there are 12 such students (8 with only a sister and 4 with a brother and a sister).

Of those 12 with a sister, there are 4 with a brother and a sister, so there are 4 out of 12 with a sister who also have a brother.

p = 4/12 = 1/3

step-by-step explanation:

you can add the two numbers and divide the result by 2. or you can find the gap between the two numbers and add half of this to the smaller number.

correct answer:

b.(19,-2)